Electrophotographic image forming apparatuses, such as a copying machine and a laser beam printer, emit light corresponding to image data to an electrophotographic photosensitive member (photosensitive member) to form an electrostatic image (latent image). Electrophotographic image forming apparatuses supplies toner or developer, which is a recording material, from a developing unit to the electrostatic image to form a toner image. This toner image is transferred from the photosensitive member to a recording medium, such as recording paper, with a transfer unit. The toner image is fixed on the recording medium by a fixing unit to form a recorded image.
For developing units using a dry one-component developing method, various apparatuses are proposed. One example is as follows: A one-component developer (toner) is placed on a developing sleeve (developing roller) serving as a developer bearing member to form a uniform toner layer by using a layer-thickness controlling member. This developing sleeve is brought into contact with a photosensitive drum serving as an image bearing member. Then, a developing bias voltage composed of, for example, a direct-current component, is applied to the developing sleeve to cause a potential difference between an electrostatic image on the photosensitive member and the developing sleeve. Thus, the toner is transferred to the electrostatic image to form a visible image.
If a developing unit is reduced in size to make the apparatus compact, also the diameter of the developer bearing member need to be decreased. Thus, decreasing the diameter of the developer bearing member may deflect the developer bearing member to cause variations in print density between the ends and the center of paper. Furthermore, the deflection of the developer bearing member will cause a greater pushing force at the ends than the center, and thus, the ends of the image bearing member in contact with the developer bearing member may be significantly worn out.
Thus, a configuration in which the central axis of the developer bearing member is inclined with respect to the central axis of the image bearing member is proposed as a measure against such deformation of the developer bearing member, as disclosed in PTL 1. This configuration allows the developer bearing member to be kept contact with the image bearing member along the longitudinal direction thereof even if the developer bearing member deflects.